A capo is a device for clamping the strings of a stringed musical instrument, such as a guitar, against the fretboard of the instrument neck in order to alter the (unfingered) pitches produced by the strings. Ordinarily, a capo is clamped between the frets along the fretboard so that the effective string lengths are determined by the adjacent fret, and the strings will produce the notes corresponding thereto.
In the past, capos have utilized various means for attaching the device to the instrument neck, including screws, levers, cams, and spring-loaded clamps, as well as other means. Spring-loaded clamps have become popular because they can be opened and rapidly moved to a new position using only one hand. This makes manipulation during a performance practical. However, one problem with prior art spring-loaded capos is that they require more hand force to open than is desirable, and it can be difficult to keep the capo open, as required, to reposition it over the strings.
As noted above, spring-loaded capos are well known, and have been described in many U.S. patents, for example, in U.S. Pat. No. 4,583,440, Powell, Jr., U.S. Pat. No. 6,008,441, Steinberger, U.S. Pat. No. 6,528,711, Paige, U.S. Pat. No. 7,566,824, Small, U.S. Pat. No. 7,745,710, Campling, and U.S. Pat. No. 7,968,778, D'Addario and Steinberger.